The ability to separate aggregate material into various components has proved highly valuable to modern industrial applications. Many different separation techniques have been utilized in the past with these techniques relying on differing characteristics of the components of the aggregate, such as size, weight, specific gravity, solubility of different solvents, etc. Metal recycling, waste handling, incineration and biofuel production represent only a few of the various industries for which magnetic separation and materials handling is needed. Depending upon the particular application, material separators may be used either individually or collectively for the purpose of separating particulate material into desired components.
It has long been recognized in certain industries, such as the paper industry and the glass recycling industry, that the separation of non-magnetic particulate material into metallic and non-metallic components based on electrical conductivities has particular utility. One type of apparatus which has been used for the purpose of separating out non-magnetic metals is known as an eddy-current separator. Eddy-current separators operate under the principle that electric current is induced within the body of a conductor when that conductor either moves through a non-uniform magnetic field or is in a region where there is a change in magnetic flux. Accordingly, eddy-current separators make it possible to separate metallic non-magnetic metals, such as aluminum, copper, zinc and magnesium, from non-metallic material, such as glass, plastic and rubber.
One type of eddy-current separator which has been used incorporates a rotating drum with an internal and independently rotatable magnetic roll to separate a mixed conglomerate of non-magnetic particulate material into these metallic and non-metallic components. More particularly, both the drum and its internal magnetic roll are journaled for rotation in a common direction about respective longitudinal axles and independently driven by separate motors. Housed within the internal magnetic roll is an array of elongated, rare earth magnets, such as neodymium. These permanent magnets are angularly spaced apart from the magnetic roll's axis and are polarized in a radial direction such that circumjacent ones of these permanent magnets have opposite poles located radially inwardly. The magnetic roll is positioned with its axle radially offset relative to the drum's axle so that the magnetic roll is positioned to have an active surface located proximate to the drum's sidewall. Further, the magnetic roll rotates at a rotational speed of approximately 400-600 revolutions per minute (rpm), or sometimes higher, to produce an oscillating magnetic field in a region therearound.
In operation, then, mixed material is introduced onto the drum's sidewall via a feeding system. As the material is fed onto the drum's sidewall, it is subjected to the oscillating magnetic field produced by the internal magnetic roll. This results in the induction of eddy-currents in those components of the particulate material which are conductive. The conductive materials are thrown in the same direction of the external drum's movement to a first location which may be either a first conveyor positioned beneath the drum or a discharge bin. Non-conductive materials are unaffected, and less conductive materials are less affected, by the oscillating magnetic field and follow the rotation of the external drum to be deposited at a second discharge location which may be a second conveyor positioned underneath the drum.
While this type of eddy-current material separator has proved useful in various industries for the purpose of separating non-magnetic material into metallic and non-metallic components, there are drawbacks in the construction of the apparatus. For example, the relatively slow angular velocity of the internal magnetic roll, coupled with the relative large mass of the permanent magnets housed therein, makes it rather difficult to produce a magnetic field which is strong enough to extend beyond the drum's sidewall and induce a sufficient amount of eddy-currents into the metallic components of the particulate material. In addition, the physical arrangement in some of these prior art eddy-current material separators is undesirable in that the permanent magnets are not distributed evenly around the internal magnetic roll which can result in balancing problems of the magnetic roll at certain angular velocities. Accordingly, the ability of these separators to efficiently separate the particulate material into desired components can be hindered.
It would, thus, be advantageous to provide a material separator, and specifically an eddy-current material separator, which has improved performance characteristics in the separation of non-magnetic particulate material. These improved characteristics can be accomplished, at least in part, by providing a magnetic roll assembly having a plurality of internal magnetic arrays, with each of the magnetic arrays rotating at a much higher angular velocity relative to the external drum to produce a superior oscillating magnetic field in the vicinity of the drum's outer sidewall surface. The present invention is directed to meeting this need, among others.